In recent years, plant factories have been attracting attention in order to supply safe food and supply foodstuffs year-round (for example, see Patent Documents 1 to 3). In the plant factory, plants are cultivated by a nourishing solution instead of soil, and furthermore plants are grown using natural light and artificial light as light sources, or using only artificial light as a light source.
Moreover, in the plant factory, temperature, humidity, sunshine duration, carbon dioxide amount, and the like are controlled, and an optimal environment for the plants is created, and thus the growth is facilitated. As a result, the plants can be cultivated to a shippable state in a short period of time. Also, the plants to be cultivated can be laid out three dimensionally, and thus the efficiency of utilizing the land can also be increased.
However, a large cost is required to construct and maintain the plant factory. Also, if power supply stops, there is a risk that the plants will die out. Therefore, it is absolutely impossible to supply food for mankind using only plant factories, and the outdoor cultivation of the plants is also important, similarly to the past.